Solid-state imaging apparatus or imaging readers, that have been configured either as a handheld, windowed, portable scanner; a stand-mounted, windowed, stationary scanner; a countertop-mounted, vertical slot scanner having a generally vertical or upright window; a flat-bed or horizontal slot scanner resting on, or built into, a countertop and having a generally horizontal window; or a bi-optical, dual window, scanner having both generally horizontal and generally vertical windows; have been used as workstations in many venues, such as supermarkets, department stores, and other kinds of retailers, libraries, parcel deliveries, as well as factories, warehouses and other kinds of industrial settings, for many years, in both handheld and hands-free modes of operation, to electro-optically read by image capture diverse indicia or targets, such as symbol targets, e.g., one-dimensional symbols, particularly Universal Product Code (UPC) bar code symbols, and two-dimensional symbols, as well as non-symbol targets, such as driver's licenses, receipts, signatures, etc., the indicia being associated with, or borne by, objects or products to be processed by the imaging readers. In the handheld mode, a user, such as an operator or a customer, held the imaging reader and manually aimed a window thereon at the indicia. In the hands-free mode, the user slid or swiped a product associated with, or bearing, the indicia in a moving direction across and past a window of the reader in a swipe mode, or momentarily presented the indicia associated with, or borne by, the product to an approximate central region of the window, and steadily momentarily held the indicia in front of the window, in a presentation mode. The choice depended on the type of the reader, or on the user's preference, or on the layout of the venue, or on the type of the product and the indicia.
The imaging reader included one or more solid-state imagers (also known as imaging sensors). Each imaging sensor included a sensor array of photocells or light sensors (also known as pixels), which corresponded to image elements or pixels over a respective field of view of the imaging sensor, an illumination assembly including one or more visible (red/white) light sources, e.g., light emitting diodes (LEDs), for illuminating the respective field of view with visible illumination light, and an imaging lens assembly for capturing return ambient and/or visible illumination light scattered and/or reflected from the indicia contained in the respective field of view, and for projecting the return light onto the imaging sensor to initiate capture of an image of the indicia. For workstations having multiple imaging sensors and multiple fields of view, the indicia often was simultaneously contained in more than one field of view during reading. The imaging sensor was advantageously configured as a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device, and included associated circuits for producing and processing an electrical signal corresponding to the indicia. The imaging sensor was controlled by a controller or programmed microprocessor that was operative for processing the electrical signal into information indicative of the indicia being imaged and read, and when the indicia was a symbol, for decoding the symbol.
The aforementioned illumination assembly was especially advantageous when the reader was operated in low light or dark environments. Yet, the use of visible (white/red) illumination light, either emitted continuously or pulsed, was sometimes perceived to be too annoyingly bright and bothersome to some operators, customers, their children, or their pets. During the swipe mode when the white/red LEDs were always on, the constant white/red illumination light was sometimes regarded as being unpleasant to some operators who were exposed to such bright white/red light for extended time periods during a work shift, thereby making the operators uncomfortable with such long term exposure to their eyes. When the white/red LEDs were pulsed, it was usually overdriven with a high drive current to produce an intensely bright white/red illumination light, again making the operators and others uncomfortable.
Accordingly, it would be desirable to counter the adverse reaction to such bright light by such techniques as driving the white/red illumination LEDs with lower drive currents, or changing their duty cycles, or using light baffles, or using different illumination sources having lower intensities and/or of different wavelengths. However, each of these techniques was problematic.
For example, some light sources were less effective in reading certain indicia, such as a bar code symbol, whose contrast varied as a function of the wavelength of the light illuminating the symbol. As used herein, the term “contrast” is defined as the difference in reflectivity/scattering properties between a symbol's bars, which are typically printed dark in color, e.g., black or blue ink, (low reflectivity), and the symbol's spaces, which are typically white in color (high reflectivity). Thus, a symbol printed with thermal ink, typically blue in color, on thermochromic paper was well detectable in white or red visible light, but was hardly, or not readily, detectable in light having a higher wavelength, e.g., infrared (IR) light. Employing IR light, which, depending on such factors, among others, as wavelength, is non-readily visible, or semi-visible, or, in some cases, invisible, to the human eye, could ameliorate the above-described adverse reaction to bright visible light, but with the drawback of not being able to effectively read thermally printed symbols. However, there are many applications where such thermally printed symbols are used. For example, delicatessen counters in supermarkets routinely thermally print symbols on labels for meat/cheese products that have been cut and weighed to order, and it is critical that such thermally printed symbols be effectively readable at point-of-transaction workstations at checkout in retail establishments, such as supermarkets.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.